A common type of door lock used in exterior doors on dwellings is a deadbolt operable by a crank or knob on the inside of the door and by a key only on the outside. An exterior door of high quality is built strong enough to resist being kicked in, but many such doors nevertheless have frangible, e.g., glass, panels built into them (or adjacent to them in the door frame). Would-be intruders can break such panels, allowing them to reach in and open the lock from the inside. One prior art solution is to provide key operation from both sides of the door. The obvious problem with this solution is that if the door is locked, it cannot be opened without a key. This poses a safety concern in an emergency. Oftentimes, residents simply leave a key in the inside keyhole, effectively converting this type of lock into the inside crank type mentioned first above.
Thus, a need exists to provide a lock that may be opened from the outside by key and from the inside by a mechanism operable in poor lighting conditions principally by a tactile process known by the residents but difficult to guess by an intruder (with, or optionally without, a key).
The typical prior art combination dial must be manipulated carefully in good light. (In this application, the word “combination” means the series of numbers and letters used to open a lock.) Most people have experienced, at some time in their lives, having to re-enter a combination multiple times because of imprecision in dialing. Such combinations ordinarily require the memorization of three double-digit numbers. These conditions can pose a difficulty for young children and for anyone trying to open the lock in low-light conditions. Therefore, a need also exists for a new type of combination mechanism for the inside that would be easy to open quickly in dim light, yet be difficult for a would-be intruder to operate through a hole in the door.